DevTools: Handle chrome://inspect page reload correctly

On page reload the existing InspectUI object is reused and
StartListeningNotifications is called more than once.
This patch makes sure that the subsequent calls work.

BUG=324768

Review URL: https://codereview.chromium.org/108053004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239477 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239477
Add images.google.com to mobile_memory Telemetry pageset.

This new test case scrolls to the bottom of images.google.com. This will
let us see the renderer private_dirty improvement (30% decrease expected) when
the discardable memory allocator is turned on as well as VM peak decreases
brought by future improvements.

BUG=299828

Review URL: https://codereview.chromium.org/98103003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239478 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239478